The crested lambeosaurine hadrosaurs displayed an enormous variety of helmets, hatchets, and hood ornaments on their skulls. As a functional piece of anatomy, the crest was part of the nose. Fossil hadrosaurs, for which a cross-section of the skull can be observed, show that the nostrils were connected to the throat by a hollow set of cavities and tubes through which the dinosaur breathed. Most other kinds of dinosaurs did not have such crests, however, so we may assume that hollow crests had a special function other than breathing. What other purpose did such a crest have?
Crests came in a number of shapes. The crest of Corythosaurus ("helmet lizard") was rounded like a dinner plate standing on end, its base being thick to accomodate air passages. The crest associated with Lam-beosaurus resembled a hatchet. The tube-like crest of Parasaurolophus was so long that it extended behind the head and over the shoulder. And the crest of the recently discovered Olorotitan looked something like a battle ax.
Many ideas have been suggested over the years for the purpose of these head crests. One early hypothesis regarding the crest of Parasaurolophus was that it may have been used like a snorkel. Because there is no evidence that these crests had a "breathing hole" at the end, however, this idea is no longer accepted.
Moreover, these crests may have had more than one function. It is likely that such a crest improved the dinosaur's sense of smell. This would have been important to relatively defenseless creatures such as hadrosaurs, allowing them to detect the scent of a predator from a safe distance.
The crest probably helped members of the same species recognize one another, a vital need for recognizing and choosing a mate. In 1975, paleontologist Peter Dodson conducted a groundbreaking study of lambeosaurine head crests and determined that they first became prominent when the animals reached the age of sexual maturity. Furthermore, females probably had smaller and differently-shaped crests than males. Although Dodson's conclusions have been universally accepted for many years, a recent study suggests that some of the specimens of "males" and "females" that he used for comparison came from different strati-graphic layers, meaning that they may not have actually lived at the same time. Nonetheless, crest shape could have helped to tell the boys from the girls, making the job of finding a mate easier. The shape and color of the crest may have made certain males or females more attractive than others. It would have also indicated the relative age and sexual maturity of an individual. In the world of animal matchmaking, those kinds of visual clues were important for bringing together healthy mates.
Another function of the crest might have been to create and project sounds, an idea that was thoroughly explored by paleontologist David Weishampel in 1981. Lambeosaurines could blow air through the tubes and hollow chambers of the crest to create bellowing sounds possibly similar to those made by an antique car horn or elephant. The sounds may have been important to hadrosaur communication. They could have used their voices to warn of approaching danger, call for help, or to express themselves for other reasons.
Knowledge of the sound-making ability of lambeosaurines was advanced in 1999 by paleontologists Thomas Williamson and Robert Sullivan, based on a new and remarkably complete skull of Parasaurolophus. Using computed tomography and modeling to examine and reconstruct the interior of the skull, the scientists not only produced a map of the interior air passages of the crest but also electronically synthesized the kinds of sounds that could be made using such a crest. Whereas previous knowledge of the Parasaurolophus crest concluded that its inner chambers simply consisted of two parallel, hollow tubes, Williamson and Sullivan revealed that the two tubes from the nostrils actually branched into as many as six tubes that were additionally interconnected to supplemental
air chambers in other parts of the crest. In addition to producing a wide variety of sounds, the paleontologists concluded that the crest may have served a thermoregulatory function. The inside of the Parasaurolophus crest was lined with blood vessels. Heat could have been collected by the crest if the head was turned toward the Sun or released if the head was held in the shadows. The air passages in the crest would have allowed the dinosaur to transfer heat more efficiently by passing hot and cold air through the head.
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technically bidpedal, the hadrosaur body plan also accommodated a part-time quadrupedal stance if needed, and these dinosaurs often are pictured using both styles of walking.
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